1. Field of the Invention
The present invention relates to a network system, and more particularly, to a method for managing system resources in a network system in which a digital interface is used for connection.
2. Description of the Related Art
Recently, a variety of types of digital devices, such as digital televisions (DTVs), digital video cameras (DVCs), digital versatile disk players (DVDPs) and digital set-top boxes, have been developed. For construction of a network of digital devices, an IEEE1394 standard which is approved as a digital interface by the IEEE committee has been considered.
In particular, in a network system in which a digital interface such as IEEE1394 is used for connection, connection management among a plurality of digital devices is defined by an IEC61883 standard. This standard defines an input plug as an inlet for receiving a bit stream and an output plug as an outlet for outputting a bit stream with respect to each digital device. This standard also defines an output master plug register (oMPR), an output plug control register (oPCR), an input master plug register (iMPR) and an input plug control register (iPCR) as registers for controlling input plugs and output plugs. Digital devices control the input and output plugs by managing registers such as oMPRs, iMPRs, oPCRs and iPCRs, thereby managing an isochronous bit stream connection between digital devices. Representative types of connection among a plurality of digital devices are point-to-point connection and broadcast connection. Point-to-point connection comprises an input plug, an output plug and a channel between the input and output plugs. A device can establish or overlay connection, perform disconnection, and release the resources which may be, for example, a channel and a bandwidth for the connection according to point-to-point connection. Broadcast connection includes broadcast-in connection and broadcast-out connection. Broadcast-in connection is connection between an input plug and a channel. Broadcast-out connection is connection between an output plug and a channel. In broadcast connection, connection can be established only by a corresponding device to actually input or output a bit stream, but a break of the connection and release of resources can be performed by another device, as well as the corresponding one, over a network.
Establishment or break of point-to-point connection and broadcast connection is performed by managing registers such as iMPR, oMPR, iPCR and oPCR. When a device needs allocation and release of resources, the device communicates with a device serving as an isochronous resource manager (IRM) in an overall network system.
FIG. 1 is a diagram showing an example of a network system in which digital devices are connected through IEEE1394. Referring to FIG. 1, a set-top box (STB) 110, which is a source device, is connected to a digital television (DTV) 100, which is a sink device, through an IEEE1394 line. The isochronous connection between the DTV 100 and the STB 110 is established such that a user selects the STB 110 from a display for source device selection on the screen of the DTV 100 using a digital television remote controller (not shown), and then software corresponding to the selection, which is internally included in the DTV 100, operates, thereby initializing the connection between the DTV 100 and the STB 110. In the usual isochronous connection between a sink device and a source device, the sink device functions as an establisher and performs allocation of system resources, which may, for example, be a channel and a bandwidth, for the connection.
The allocation of system resources is achieved by communicating with an isochronous resource manager (IRM) in a network. When the allocation of a channel is required of the IRM, the IRM allocates a channel which is available presently. In the allocation of a bandwidth, a device which requires the allocation of a bandwidth computes the bandwidth desired. Then, the computed value is suggested to the IRM, and whether a bandwidth corresponding to the computed value is presently available is inquired. If the bandwidth is available, the bandwidth is used after the IRM is informed that the bandwidth will be used.
In FIG. 1, the DTV 100 corresponds to a device establishing an isochronous connection. For the allocation of a bandwidth, the DTV 100 primarily computes the bandwidth required for isochronous connection with the STB 110. In computing the bandwidth, more specifically, a bandwidth unit defined by the IEEE1394 standard, the DTV 100 reads the oPCR of the STB 110 and analyzes the values of fields of the oPCR, such as overhead identifier field Overhead_ID, data rate field and payload field. Then, the required bandwidth is computed according to the following formula defined in IEC61883 Part 1 Section 7.7.
BWU: IEEE1394 bandwidth unit
DR: data rate coefficient (16 for S100; 8 for S200; 4 for S400)
IF (oPCR.Overhead_ID>0)                BWU=32* oPCR.Overhead_ID+(oPCR.Payload+3)*DR;        
ELSE                BWU=512+(oPCR. Payload+3)* DR;By doing this, the DTV 100 computes the bandwidth required for connection with the STB 110 and uses the bandwidth for the connection when an IRM allocates the computed bandwidth to the DTV 100 in a network.        
After an isochronous connection between the DTV 100 and the STB 110 is established, a user can view the selected programs, which are received from the STB 110, on the screen of the DTV 100. Thereafter, when the user operates a set-top box remote controller or a digital television remote controller (e.g., to turn off the power of the STB 110 or the DTV 100, or to select another device from a display for source selection on the screen of the DTV 100), the connection between the STB 110 and the DTV 100 is broken and system resources used for the connection are released. Since it is the DTV 100 which establishes the connection, it is also the DTV 100 which releases system resources. In other words, the DTV 100 communicates with an IRM and releases the channel and the bandwidth which were used for the connection.
A conventional isochronous connection method between a source device and a sink device has several problems. The conventional isochronous connection method does not define a solution for the case in which the bandwidth of an output bit stream changes according to the characteristics of a source device. For example, different bandwidths are required for transmission of an output bit stream by a set-top box, a digital television, etc., when the bit stream to be received or reproduced is of digital video (DV) format, when the bit stream is of motion picture experts group (MPEG) format, when an MPEG format is a standard definition (SD), and when an MPEG format is a high level definition (HD). Presently, there is no teachings regarding how a bandwidth is allocated and released in this case. For the stability of an overall IEEE1394 network system, a source device establishes its registers base on the maximum bandwidth which the source device can cover. Then, a sink device is allocated the maximum bandwidth by an IRM in a network based on the registers of the source device, and releases the maximum bandwidth when breaking the connection later. However, this method for allocation/release of a bandwidth has a problems in that system resources are very inefficiently used. In other words, although many devices, for example, ten or more devices, may be connected, the connection of only a small number of devices, for example, three devices, exhausts system resources in a network by allocating a maximum bandwidth to each device. Consequently, only a small number of devices can be connected and operated.